Is it correct to say "Allah and His Messenger know best" after the death of the Prophet (peace and blessings be upon him)?

Question:
Regarding the phrase "Allah and His Messenger know best" after the death of the Prophet (peace and blessings be upon him), is it said only for matters of religion? Is it said in such cases because the Messenger (peace and blessings be upon him) was the most knowledgeable of creation regarding the Shari'ah of Allah?

Answer:
My brother, let us leave this philosophy. The scholars say that this phrase is used during the lifetime of the Messenger of Allah: "Allah and His Messenger know best." After the death of the Messenger, they say "Allah knows best," because the Messenger (peace and blessings be upon him) does not know what has happened after him. Allah says to him on the Day of Resurrection, if people are turned back from the Sirat, and he says (peace and blessings be upon him), "My Ummah, my Ummah," and Allah says to him: They have continued to be apostates. So I say, "Woe, woe to those who changed and altered." Therefore, after the death of the Messenger, he (peace and blessings be upon him) does not know.